Findings may affect how women are
treated for bone fractures
Sept.25, 2008

Women’s
muscles may require longer, more
intensive rehabilitation
after bed rest and cast immobilization,
as reported today by the Institute for
Neuromusculoskeletal Research at the
Ohio University Heritage College of Osteopathic
Medicine (OU-HCOM).

According to Brian C. Clark, Ph.D.,
assistant professor of neuro-muscular
biology, the discrepancy may relate to
how sex-specific hormones regulate the
growth of muscle mass. The study is the
first to report sex differences in
muscle strength restoration following
immobilization of a limb.

“Our
findings may have important implications
for how women are
treated for fractures, including more
and/or different rehabilitation
methods,” Clark said.

Clark
worked on the study with Ohio University
researchers Richard L. Hoffman and David
W. Russ, Ph.D., as well as Todd M.
Manini, Ph.D.,
of the University of Florida. The team
discussed their findings this week at
the Integrative Biology of Exercise
meeting, hosted by the American
Physiology Society (APS) in Hilton Head,
S.C. A report of their preliminary data
will appear in an upcoming issue of
Archives of Physical Medicine and
Rehabilitation.

The
researchers set casts to the
non-dominant wrists and hands of 10
healthy volunteers – five men and five
women – for three weeks. Wrist muscle
strength was measured prior to placement
of the casts, weekly during
immobilization and one week after cast
removal. Researchers also used
electrical stimulation to induce muscle
contractions, which showed how well the
participants’ nervous systems were able
to activate their wrist muscles.

Results
showed that men and women lost muscle
strength at similar rates during
immobilization. But within one week of
cast removal, the men’s strength
returned almost to pre-cast levels,
while the women’s strength levels
remained 30 percent lower than normal.

Immobilization did reduce the ability of
the nervous system to activate wrist
muscles, and the response was similar in
men and women, suggesting that the
slower restoration of strength among
women is more likely due to different
rates of muscular strength-building, as
opposed to differences in the nervous
system.

According to a 2003 World Health
Organization report, women are four
times more likely than men to experience
forearm fractures requiring cast
immobilization, and almost 50 percent of
women will experience a bone fracture at
some point in their life.

Clark
cautioned against over-interpretation of
the study results because of the
relatively small sample size. “Our
findings indicate that more work needs
to be done to confirm and understand the
reasons for these sex differences, the
extent to which they occur, and the
underlying mechanism,” Clark said.

Clark
and his colleagues have begun the next
phase of this research, which they hope
will provide more comprehensive answers.